Britain said today that there was no need for Washington to mediate on sovereignty in the simmering stand-off with Argentina over the Falkland Islands, as it was simply not up for discussion.

London said there was nothing to mediate over on sovereignty because the 3,000-odd Islanders wished to remain British.

During a visit to Buenos Aires yesterday, US Secretary of State Hillary Clinton offered to help resolve the row by encouraging dialogue, but balked at an Argentine request for US mediation.

An infuriated Argentina ramped up its affirmations of sovereignty over the South Atlantic Ocean islands after a British firm began drilling for oil in Falklands waters last month.

"We are of course in regular touch with United States on this issue as on so many others," said a Foreign Office spokeswoman.

"This is a familiar US position. The United States recognises UK administration. We recognise the goodwill that exists around this issue.

"The question is not the lack of a mediator: the principle of self-determination applies, the Islanders wish to remain British, and so we cannot legitimately negotiate on sovereignty."

On direct US involvement, Prime Minister Gordon Brown's spokesman said: "We don't think that's necessary".

"We welcome the support of the secretary of state in terms of ensuring that we continue to keep diplomatic channels open but there is no need for that," he told reporters.

Foreign Secretary David Miliband on Tuesday updated the British Cabinet on the latest developments.

Brown's spokesman said Miliband had stressed to the Cabinet that "self-determination of Islanders is the key issue".

"He emphasised that we have a strong ongoing working relationship with Argentina, particularly around G20.

But Britain believed the oil drilling was "both the right thing to do and is entirely legitimate"," the spokesman added.

Argentina and Britain went to war over the islands in 1982. Britain successfully reclaimed them following an Argentine military invasion.